In the related art, a substrate processing step for forming a thin film on a substrate has been performed as a step of a manufacturing process of a semiconductor device, e.g., a DRAM. The substrate processing step is performed by a substrate processing apparatus that includes a cassette mounting unit configured to mount a process substrate cassette for accommodating a plurality of process substrates therein and a dummy substrate cassette for accommodating a plurality of dummy substrates therein, a process chamber in which at least one of the process substrate or the dummy substrate is processed, a gas supply unit configured to supply a process gas into the process chamber, an exhaust unit configured to exhaust an inside of the process chamber, and a transfer unit configured to transfer the substrates between the cassette mounting unit and the process chamber.
In this case, a dummy substrate may be repeatedly reused in a subsequent substrate processing. That is, for example, when the substrate processing involving a film forming process is performed, residues are generated during the film forming process and form a deposited film. Each time the dummy substrate is reused, the deposited film is accumulated on the dummy substrate. Accordingly, in order to prevent film separation caused by an increase of a cumulative thickness of the deposited film or to prevent warp or deformation of the dummy substrate caused by a stress of the deposited film, the dummy substrate is replaced once the dummy substrate is used more than a predetermined number of use (e.g., use frequency) or if the thickness of the deposited film becomes greater than a predetermined value (e.g., cumulative thickness value). In a manufacturing line of a factory, if a cumulative thickness of a deposited film of at least one of dummy substrates accommodated in a dummy substrate cassette exceeds a predetermined cumulative thickness value, the entire dummy substrate cassette is replaced (e.g., all dummy substrates are either discarded or reused). Thus, it is advisable that the dummy substrates are used in such a way that each dummy substrate has the similar use frequency or the cumulative thickness. Accordingly, for example, the dummy substrates are selected and used based on the cumulative thickness value of the dummy substrates or the like so as to effectively use the whole dummy substrates accommodated in the dummy substrate cassette.
Sometimes, a management error may occur, e.g., an error of not timely replacing a dummy substrate cassette when the dummy substrate cassette needs to be replaced because a predetermined number of dummy substrates have a thickness greater than a predetermined cumulative thickness value. Due to the management error, the substrate processing may continuously be performed using the dummy substrates whose thickness exceeds a predetermined cumulative thickness value. In such a case, a film separation may be caused by an increase of a cumulative thickness value, and particles may be generated within a process chamber, thereby deteriorating a substrate processing quality.
Therefore, it is an objective of the present disclosure to provide a substrate processing apparatus, a semiconductor device manufacturing method and a substrate processing method, which can prevent the generation of particles and improve the quality of the substrate processing.